Weak tests incompatible with V8 change #995

A recent V8 change, 4733273: [heap] Disallow JS execution in second pass callbacks., makes a strict change to WeakCallbackInfo::SetSecondPassCallback:

The second pass callback is prohibited from executing JavaScript. Embedders should schedule another callback in case this is required.

This condition is enforced at runtime and results in a crash. This change conflicts with NAN's weak tests, both written to run JS in the weak callback.